There are neurons in the hippocampus of rats (and other mammals) that have the remarkable property of location-specific firing. A given 'place' cell will fire only when the rat is in a circumscribed part of its current environment, largely independent of what the rat is doing there. The properties of place cells will be thoroughly investigated by recording single neurons in freely-moving rats and using a quantified, computer-operated data collection system. Our immediate goals are to: 1) Investigate the extent to which the geometry of an anvironment controls the firing of place cells. 2) Investigate the extent to which the specific stimuli within an environment control the firing of spatial cells. 3) Determine the spatally-specific firing properties of other anatomically and physiologically identifiable cell types. 4) Attempt to explain differences in spatial firing among hippocampal cell types on the basis of known anatomy and synaptic connectivity. 5) Measure temporal and spatial relationships for the firing of pairs of neighboring hippocampal cells. These data will help us achieve goal 4. 6) Find ways of modifying spatially-specific firing manipulating the geometry and contents of recording environments. Our long-term goal is to understand how the properties of physical space are represented in the neural space of the hippocampus.